1. Field of the Invention
The present invention relates to an ink jet head, and more particularly to an ink jet head used in an ink jet type printer for ejecting ink to print an image on a recording medium.
2. Description of the Related Art
Non-impact type printers are replacing impact type printers and assuming an increasingly large share of the printer market. Ink jet printers can be raised as the non-impact printer that has the simplest concept and that moreover is easy to apply for multi-tone and color printing.
Japanese Patent-Application Publication (Kokai) No. HEI-10-272770 (corresponding to copending U.S. application Ser. No. 09/049,046) discloses an ink jet head used in an ink jet printer. The head includes an actuator and a manifold connected to the actuator. The actuator is formed with a plurality of ink channels aligned in a row. Each ink channel has an ink inflow port at one end and a nozzle at the other end. The actuator drives the ink channels to eject ink through the nozzles. The manifold is connected to the ink inflow port end of the actuator for supplying ink into the ink channels. The manifold is formed with a supply channel that extends parallel with a direction in which the row of the ink channels extend, and that is in fluid connection with all the ink inflow ports of the ink channels.
Generally, miniscule bubbles are dissolved in the ink supplied to the ink jet head. Dust and other debris are also mixed in the ink. The such air bubbles can grow and clog the ink channels, and the debris can cause defective ink ejection, that can degrade print quality.
In order to overcome these problems, well-known purge operations are performed to recover and maintain the ink ejection function of the ink jet head. Specifically, in a purge operation, a suction cap is brought into contact with the nozzle surface of the ink jet head. A suction pump connected to the suction cap is driven to generate large negative pressure in the suction cap. As a result, a predetermined amount of ink, along with air bubbles and debris, is sucked from the interior of the ink jet head through the suction cap. In this way, the ink in the ink channels and supply channel is replenished and the air bubbles and debris are discharged through the suction cap.
However, it is difficult to remove a relatively large air bubble from the above-described ink jet head because of the following reason.
FIGS. 17(a) and 17(a′) show an ink inflow port of an ink channel 131 and an air bubble EB contained in an supply channel 141 of the above-described ink jet head. During the purge operation or flushing operation, ink in the supply channel 141 flows into the ink channel 131. In accordance with this, the air bubble EB, which has a relatively large size, is drawn toward the ink channel 131 and clings to the ink inflow port of the ink channel 131 as shown in FIGS. 17(b) and 17(b′). At this time, the bubble EB will only seal a portion of the inflow port, and generates an unsealed portion 131a at the inflow port. Because the inflow port of the channel 131 is formed in a flat surface, the unsealed portion 131a provides a broad space around the air bubble EB. As a result, the ink will freely flow through the unsealed portion 131a. 
Moreover, when the air bubble EB is slightly sucked into the channel 131 as shown in FIG. 17(b), its change in the surface area is rapid, so that a great surface tension is generated on the air bubble EB. The surface tension functions to restore the spherical shape of the air bubble EB.
Because of these reasons, the air bubble EB can not easily be sucked into the in channel 131. Therefore, even if purge and flushing operations are repeatedly performed, the air bubble EB will not be successfully discharged. This will cause insufficient ink supply to the ink channel 131 or improper ejection, thereby degrading quality of printing.